Copper-based low temperature shift catalysts have been well studied in the art. For example, see the article "The Water Gas Shift Reaction" by David S. Newsome, CATAL. Rev.-SCI. ENG., 21(2), 275-318 at pp. 296-303 (1980). The above referenced article also indicates that oxides of calcium and magnesium have been added to copper-zinc-chromium catalysts with inconsistent results with regard to activity and temperature stability.
It has been found that when a rare earth promoter and an alkaline earth compound is added to a copper-zinc catalyst, the resulting composition has an enhanced activity and a high resistance to poisoning by chlorine-containing compounds.